The host immunologic response to oral microorganisms may play a significant role in the pathogenesis of periodontal diseases. It is not clear whether this response is primarily protective or at times may have destructive components. In the present investigation, the humoral and cellular immunologic response to the predominant microorganisms isolated from sites of active destruction will be determined. Samples of saliva, blood, and gingival tissue from the diseased site(s) will be collected prior to and after therapy. Individual microbial species present in destructive and nondestructive sites will be compared for their relative ability to stimulate local and/or systemic cellular/humoral immune response. Reactions to a standard battery of suspected periodontopathic microorganisms will also be determined to provide some cross-sectional information between various patients in the studies. However, the priority analyses will be to antigens of the host's indigenous microbiota. Computer-assisted analyses of changes in immunologic responses will be compared to changes in microbial composition and clinical status of disease. Also, the effect of both mechanical and/or antibiotic therapy on these responses will be determined longitudinally for the individual patients. Any consistent patterns in immunologic responses to the microbial antigens may be useful in determining etiologic agent(s) of specific periodontal diseases. It is conceivable that imunologic responses may reflect altered host-microbe interactions that precipitate the onset of disease. Thus, the use of changes in antibody levels or in cellular immune responses to suspected pathogens as an in vitro laboratory diagnostic test can be evaluated.